Polylactic acid(PLA) resin is a plant-derived resin which can be obtained from plants such as a corn, and has a biodegradable property. Compared with conventional petroleum resins such as polystyrene resin, polyvinylchloride(PVC) resin, polyethylene resin, and so on, the polylactic acid resin is advantageous in saving petroleum resources, preventing discharge of carbonic acid gas, and thereby decreasing environmental pollution. Recently, environmental pollution by waste plastics becomes one of social problems. Thus, instead of conventional plastics (petroleum resin), it is tried to use the polylactic acid resin in the areas of food packages and containers, cases for electronic devices, and so on. However, compared with conventional petroleum resins, polylactic acid resin is not satisfactory in their impact resistance and heat resistance.
To solve these drawbacks, polylactic acid resin is blended with one or more conventional petroleum plastic resins. For example, in Korean patent Laid-open No. 10-2005-0056021, polylactic acid resin and polycarbonate resin are blended to make up for the low impact resistance and heat resistance of polylactic acid. However, in this case, as the amount of blended polycarbonate resin increases to increase the impact resistance and heat resistance, the portion of the petroleum plastic resin increases, and the portion of polylactic acid resin decreases in the blend. Thereby, the aim of using polylactic acid is not sufficiently fulfilled.